One of the key components of a computer system is a place to store data. Typically, computer systems employ a number of storage means for archiving information and data. One place a computer can store data is in a disk drive, which is also called a direct access storage device.
A disk drive or direct access storage device includes one or more disks which look similar to 45 rpm records used on a record player, or compact disks which are used in a CD player. The disks are stacked on a spindle, much like several 45 rpm records waiting to be played. In a disk drive, however, the adjoining disks are mounted to the spindle and spaced apart so that the separate disks do not touch each other. Currently, available disks are about 21/2" and 31/2" in diameter. Disk drives having smaller diameter disks are also currently being worked on by many in the industry.
The surface of each disk is smooth and uniform in appearance. Data on the disks in a disk drive is not stored in grooves. Each of the surfaces is, however, divided into portions where data is stored. Each disk surface has a number of data tracks situated in concentric circles like rings on a tree. The tracks on the disk essentially replace the grooves in a 45 rpm record. Each track in a disk drive is further subdivided into a number of sectors which is just one portion of the circumferential track.
Disks in a disk drive are made of a variety of materials. The substrate or inner core can be made of glass, plastic or metal. In the case of magnetic recording, a magnetizable layer of metal is placed on the substrate or inner core. Data is stored on such a disk by magnetizing a portion of the magnetizable layer of the disk. The portion magnetized will be one or more of the sectors mentioned above. The data is usually transformed or encoded into a more compact form before it is recorded on the disk.
In order to magnetize the surface of a disk, a small ceramic block containing an electromagnetic transducer known as a read/write head is passed over the surface of the disk at specific tracks and sectors. More specifically, the read/write head is flown at a height of approximately six millionths of an inch or less from the surface of the disk as the read/write head is energized to various states causing a domain within a sector in the track below to be magnetized.
To retrieve data stored on a magnetic disk, the read/write head is flown over the disk. The small magnetized portions of the disk induce a current in the read/write head. By looking at current from the read/write head and decoding the pattern, the data can be reconstructed and then used by the computer system.
Like a record, both sides of a disk are generally used to store data or other information necessary for the operation of the disk drive. Since the disks are held in a stack and are spaced apart from one another, both the top and the bottom surface of each disk in the stack of disks has its own read/write head.
The ceramic block and the magnetic transducer it holds are moved over the surface of a disk using an actuator arm that compares to the tone arm in a stereo record player. The actuator arm, holds all the transducers or read/write heads, one head for each surface of each disk, in a structure that looks like a comb. The structure is also commonly called an E block.
Problems can occur in a disk drive when the electrical charge on the disk or disks differs from the electrical charge on the read/write heads. In a disk drive, the magnetic disks rotate as the read/write heads are passed over the disks. Such different amounts of electrical charge can be due to static electricity buildup due to the rotation of the disks or due to an electrostatic discharge to the disk drive. The electrical charge of the read and write elements and the electrical charge of the disks can also differ if the read and write elements are biased electrically. When using some types of read and write elements, such as those associated with a magneto-resistive head, the elements are biased or electrically charged so they work properly.
The problems that can occur when the electrical charge on the disk is different from the electrical charge on the read/write element or on the slider include the electrostatic discharge or a spark jumping across the space between the read/write elements and the disks. Such a spark may damage the magnetized portions of the disk resulting in loss of data. Likewise, the read/write elements of the heads are often destroyed during such events. Loss of data or the read/write heads for reading data or writing data is very undesirable.
Currently, many disk drives have a spindle assembly which includes a fixed shaft. The spindle assembly also includes a hub attached to the shaft so it can rotate about the shaft. The disks are attached to the hub. The hub rotates with the aid of two sets of spindle bearings and spindle races. A motor inside the spindle assembly turns the hub and the disks attached to the hub. The internal space of the spindle assembly which houses the motor is sealed from the atmosphere surrounding the disks using a seal containing a liquid which conducts electricity. Currently, the electrical path used to prevent different electrical charges on the disks as compared to the read and write elements has been the electrical path through this seal. The resistance to the flow of electrical current from the motor hub to the shaft changes drastically since the balls in the spindle bearings sometimes make contact between the hub and the shaft races. When the ball bearings do not make this contact, the fluid's resistance to the flow of electricity is very high (in the mega-ohm range) and is not low enough to always prevent an undesirable electrostatic discharge between the disks and the read/write elements of the heads. In addition, the electrical path through the seal does not prevent an unwanted electrical charge differential between the read/write elements of a sensitive magneto-resistive head and the disks.
Another apparatus used to ground a rotating spindle shaft for a disk drive without an in-hub motor is shown in U.S. Pat. No. 4,623,952 issued to Paxton. A leaf spring includes a tab that rides on the end of the rotating shaft provides an electrical path between the spindle shaft and the disk enclosure. This requires the shaft to extend to the outside of the disk enclosure. In addition, the spindle shaft must be rotating. In addition, this design adds height to the disk drive and wastes precious space, especially considering some of today's disk drives are one-half inch high.
In other art areas, slip rings have been used to provide an electrical path between a stationary member and a rotating member; however, slip rings are generally not adapted for high-speed, ultra-low wear applications such as a disk drive. In a disk drive, disks attached to a hub travel at 3,600 or greater revolutions per minute. In other art areas, such as brushes for large motors, the contact force on the shaft is not conducive to long wear or long life. The large forces used assure contact so that signals may be passed across the brush. The large forces also result in high wear, a relatively short life, and high amounts of debris from the wear.
Since the fluid seal's resistance is high and there is no low resistance ground path to prevent undesirable electrostatic events, there is a need for providing a reliable, electrical path between a disk in a disk drive and the head and the read/write elements housed therein. There is also a need for a device that is adapted for the high speeds and low wear necessary for a disk drive. Such a reliable, electrical path would prevent differences in electrical potential when comparing the electrical potential of the read and write elements to the electrical potential of the disk or disks. Furthermore, there is a need for providing an electrical path capable of having low wear and a long life and adapted to a high speed application.